Rotary combines having a rotary crop-processing unit are well known. Examples are shown in U.S. Pat. Nos. 5,445,563 and 5,688,170 assigned to the assignee of the present application. These two patents both disclose rotary crop processing units having two or more sections. The relationship between the rotor axis and the housing axis varies from one section to the other. In both of these patents, the rotor axis becomes increasingly offset from the housing axis in the crop flow direction from the housing inlet to the housing outlet. This is accomplished by abrupt transitions in the housing structure between sections where the housing shape changes. As the housing shape changes, the housing axis steps upward relative to the rotor axis and the gap between the rotor and the top of the housing increases at each step in the housing.
In a co-pending patent application, also commonly assigned, Ser. No. 378,773, filed Aug. 20, 1999, the rotor and the housing are both generally cylindrical and are arranged such that their axes are nearly concentric at the inlet and diverge in the crop flow direction with the housing axis diverging upward from the rotor axis in the to produce a gradual increase in the gap between the rotor and the top of the housing in the crop flow direction.